1. Field of the Invention
The present invention relates to a semiconductor light-emitting element such as a light-emitting diode (LED), a semiconductor laser (LD), etc., and to a method of manufacturing the semiconductor light-emitting element.
2. Description of the Related Art
A light-emitting diode of high luminance is conventionally constructed such that a light-emitting portion constituted by a double-hetero structure, etc., is disposed on the surface of a semiconductor substrate, and a current diffusion layer is deposited on the light-emitting portion. As this light-emitting diode is packaged by resin, the upper portion of the current diffusion layer is covered with a transparent resin layer to protect the light-emitting element.
In the light-emitting diode constructed in this manner, the critical angle between the current diffusion layer (refractive index 3.1-3.5) and the layer of the transparent resin (refractive index about 1.5) is within the range of 25 to 29 degrees. Light having a larger incidence angle than this critical angle is totally reflected, thus greatly degrading the probability of the light being emitted from the light-emitting element. Therefore, the extraction efficiency of the light that can be actually generated from the light-emitting diode is as low as 20% or so at present.
Incidentally, as for the method of roughening the surface of the current diffusion layer, there is known a technique of treating the surface of the current diffusion layer with hydrochloric acid, sulfuric acid, hydrogen peroxide or a mixed solution comprising these chemicals, thereby obtaining a surface-roughened chip (Japanese Patent Unexamined Publication (Kokai) 2000-299494 and Japanese Patent Unexamined Publication (Kokai) H4-354382). These methods are however accompanied by the problem that due to the influence of the crystallinity of the substrate, the roughening of the surface of the current diffusion layer may become impossible depending on the orientation of the surface being exposed. Therefore, roughening of the surface of the chip may not necessarily be possible, so that, the extraction efficiency of the light is prevented from being improved, thus making it difficult to enhance the luminance of the light-emitting diode.
As described above, the conventional light-emitting diode packaged by resin is accompanied by the problem that the incident light to be entered obliquely into the interface between the uppermost layer of the semiconductor multi-layer including a light-emitting layer and a transparent resin is totally reflect from the interface, thus degrading the light extraction efficiency of the light. Further, this problem is not limited to a light-emitting diode, but is also applicable to a surface-emitting type semiconductor laser.